Facts

What are corals?

Corals are invertebrate animals belonging to the phylum Cnidaria (from the Greek word 'Cnidos' meaning stinging nettle). There are five main classes of Cnidaria:

• Anthozoa - true corals, sea anemones and sea pens
• Hydrozoa - hydroids, siphonophores and many medusae (jellyfishes)
• Cubozoa - box jellyfishes (‘sea wasps’ and Irukandji)
• Scyphozoa - true jellyfishes
• Staurozoa - stalked jellyfishes

Blue maomao and cabbage coral

Species referred to as corals occur within in the Anthozoa and Hydrozoa. They can exist as individuals or in colonies. Many secrete calcium carbonate external skeletons.

Black corals

Black corals belong to the order Antipatharia within the Anthozoa. They are named for the dark colour of their hard proteinaceous skeletons. When alive the skeleton is covered by living tissue and bears tiny polyps. The tissue covering the skeleton can be variously coloured. Consequently living black coral colonies do not look black. For example, Antipathes fiordensis typically appears white when alive. Colonies of black coral can look like trees, whips, fans or feathers. Some species may live for hundreds of years, and may grow over three metres tall.

About 58 black coral species are known in New Zealand waters. Although their depth and geographic distributions have not been analysed in detail most appear to live between 200 and 1000m depth. Divers are most likely to encounter black corals below 40m depth on offshore reefs in northern New Zealand. In Fiordland and parts of Port Pegasus, Stewart Island, Antipathes fiordensis may occur as shallow as 10m depth.  Several subtropical species are found on shallow reefs at the Kermadec Islands.

Red corals

Although a variety of corals are red or reddish in colour, the species formally known as red corals are members of the order Anthoathecatae (hydrocorals or stylasterid corals) within the Hydrozoa. The skeletons of hydrocorals are distinguished from those of stony corals by generally being much smaller, less robust, and minutely porous and pitted with small holes for the polyps. These holes lack the distinctive vertical radial partitions (septa) that characterise stony corals.

New Zealand’s hydrocoral fauna is one of the most diverse in the world, and 80% of the more than 50 species that live here are endemic. The most familiar species is the native red coral Errina novaezelandiae (family Stylasteridae), which may be encountered in relatively shallow water (30-50m depth) in Fiordland. Concentrations of Errina species have been reported in deepwater around the Chatham Islands and off the West Coast in the South Island.

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